78 TMK MKTALUTIKSY OF ANTIMONY.-

The product of oxidising roasting may hr «ntlu>r Ui« ntablo
tetroxide (Sb204) or the volatile trioxide (SI*,/),,). Tho laittw tm'lhod
is called "volatilising roasting" (Germ. wrJliiekUymd* AWwwy), and
will be treated under tho next heading.

The chemical changes which take plaoo for tho production of tho
stable tetroxido are as follows :— Whon antimony glanw* in hwt«»d not
much above 350° C., the trioxido in forwud, with the ovulution of
sulphur dioxide :

A part of the trioxido is further oxidised to tin* peutoxidc, Hl»a()ft,
which, combining with some of tho trioxido, forum thu totroxidu,
Sb204. When oxides of metals are prowmt, anliwoniaUm ara formed.
If the ore contains a largo qimntityof Biilphidoa of foreign mutato,
which would, under ordinary oiroumHtanoos, form wilphatt.% if
they alone were calcined, antimoniatoH of tho foreign rnutalH arc?
formed.
The roasted mass should contain tho lotroxido principally, if
the ore is comparatively pure and if tho oorroofc tomporaturo
and proper quantity of air have boon maintained throughout tho
process of roasting. But ideal conditionM art* very iwtdom mot
with; hence the product may contain antimony gliiHH, undo*
composed sulphide, and antimoniatow, aracHdatiw, and nulphatoH of
foreign metals, if the ore contains those foroi^n nulpiudoH and
arsenic compounds.
According to Bidon, the proper tomporaturu for roantiug ftnti"
mony glance is about 350° 0. ; if tho tomporature in too low, the*
sulphide is not decomposed, and eonHoquontly antimony IK
formed from the mechanically malting togothor of tho nnlphido and
the trioxide at a dark red-heat ; and if the temperature is too high,
the mass begins to frit together, thereby preventing tho pcuu* tuition
of air to the interior of the mass, and both tho sulphide and the
oxide are volatilised.
The fritting of the mass during roasting can be pnwwtcHl by
constant and regular rabbling. The preuonoo of ganguo Imn a good
effect in obviating, partially at least, this difficulty. This accotlntfl
for the fact that, tho richer the oro is, tho moro ditlioult it ii to
roast. But, with rich ores, it is impOHsiblo to prevent to «omo
extent the loss due to the liquation of tho sulphide and tho formation
of flue dust, which mainly consists of tho trioxido, tho tetroxido, the
sulphide, arsenic compounds, and carbonaceous matter. Towards
the end of roasting the temperature can bo raised a little, in order